The present invention relates to a duplexer using a dielectric block and, more particularly, to a duplexer with stepped impedance resonators.
Recently, in radio communication systems, transmitting frequency and receiving frequency have been used in a similar band for improving usefulness of frequency. For high frequency circuits of these communication systems, transmit-receive branching filters have been widely used.
A duplexer, which is one of these transmit-receive branching filters, must have the excellent attenuation characteristics at receiving and transmitting terminals. The transmitting filter needs the excellent attenuation characteristics in the frequency band (receiving frequency band) higher than the pass band, but the receiving filter needs the excellent attenuation characteristic in the frequency band (transmitting frequency band) lower than the pass band. Further, with the miniaturization of the communication systems, small-sized and light dudlexers are required.
A conventional duplexer using a dielectric block is shown in FIG. 1, wherein the conventional duplexer is formed by an integrated structure having a dielectric block 100 and a plurality of resonators 111 to 120 formed therein. In FIG. 1, the duplexer has four resonators 111 to 114 for transmitting filters, five resonators 115 to 119 for receiving filters, and one resonator 120 for a branch circuit separating transmission signals from receiving signals.
The dielectric block 100 includes apertures corresponding to the resonators 111 to 120 and the apertures extending from one surface, that is, a top surface, to an opposite (bottom) surface, are arranged in a line in parallel with each other. All the surfaces of the dielectric block 100, except the top surface thereof, and inner surfaces of the apertures are coated with a conductive film. Then, the bottom surface of the dielectric block 100 acts as a shorted portion connected to a ground voltage level and the top surface thereof forms an open ended portion and then the aperture acts as a resonator of xc2xc wavelength. Also, This resonator is the UIR (uniform impedance resonator) having the same impedance in the open ended portion and the shorted portion.
Conductive rods 131 and 141 for input and output terminals are inserted into the apertures of the first and last resonators 111 and 119, respectively, and dielectric materials 132 and 142 for a capacitive coupling are formed between the conductive film formed on the inner surfaces of the apertures and the conductive rods 131 and 141. At an antenna terminal 121, the resonator 120 is used as a branch circuit for the impedance matching in the transmitting terminal and the receiving terminal. Accordingly, an input signal, which is input into the filter of the transmitting terminal, is not transmitted to the receiving terminal but the antenna terminal 121 and an input signal from the antenna terminal 121 is not transmitted to the transmitting terminal but the receiving terminal.
In the above duplexer, the coupling between the resonators is accomplished by a single coupling line in which admittance in the odd and even modes of the open ended portion and the shorted portion is constant and, except the top surface of the dielectric block, all the surfaces thereof are coated with a conductive film.
Shown in FIG. 3 is an insertion loss characteristic graph at transmitting and receiving terminals using the duplexer of FIG. 1. As shown in FIG. 3, there is scarcely any attenuation characteristic at frequency higher or lower than its pass band.
However, in the mobile communication, the transmitting frequency band is near to the receiving frequency band for effectively using the frequency band and it is required that the band-pass filter at the transmitting terminal has the attenuation characteristics at frequency higher than the pass band width to increase the attenuation at frequency next to it. Also, the receiving terminal requires the band-pass filter to have the high attenuation characteristics at frequency lower than the pass band width.
If the number of resonators increases to improve the attenuation characteristics at this band-pass filter, the insertion loss and the size of the filter may increase. Accordingly, a filter having a pole, which cuts off signals at a specified frequency without increasing the number of resonators, has be needed.
FIG. 2 is a perspective view illustrating another conventional duplexer having shorted resonators of xc2xc wavelength and massive elements such as inductor and capacitor.
Referring to FIG. 2, a filter at a transmitting terminal uses three separate resonators and a chip capacitor 211 is formed between a resonator 251 and an input terminal 231. At the transmitting terminal, the coupling between the resonators is obtained through external chip capacitors 212 and 213 which are formed on the printed circuit board (PCB) 210 and electrically connected to each other by electrical patterns formed thereon. To cut off signals at a specified frequency, a chip inductor 232 is formed at an open ended resonator 252. That is, by connecting the inductor 232 to the open ended resonator 252, the frequency, at which the impedance of the resonance circuit is xe2x80x9c0xe2x80x9d, exists at frequency higher than the resonance frequency. At this time, since the signal from an input side flows into a ground voltage level through the resonance circuit, the pole frequency to cut off an output signal is produced. Since this pole frequency is generated at higher frequency than the pass band width of the transmitting filter, the attenuation of the receiving frequency signal may be increased.
A filter at a receiving terminal employs four separate resonators 254 to 257 and a chip capacitor 217 is formed between a resonator 257 and an output terminal 241. At the receiving terminal, the coupling between the resonators is obtained through external chip capacitors 214 to 216 which are formed on the printed circuit board (PCB) 210 and electrically connected to each other by electrical patterns formed thereon. To cut off signals at a specified frequency, a chip capacitor 242 is formed at an open ended resonator 255. Accordingly, the frequency, at which the impedance of the resonance circuit is xe2x80x9c0xe2x80x9d, exists at frequency lower than the resonance frequency. At this time, since the signal from an input side flows into the ground voltage level through the resonance circuit, the pole frequency to cut off an output signal is produced. Since this pole frequency is generated at higher frequency than the pass band width of the received signal, the attenuation of the transmitting frequency signal may be increased.
Further, a chip inductor 222 and a chip capacitor 223 are used for matching the impedances of the antenna terminal 221 and the filters at the transmitting and receiving terminals. Accordingly, the signal which is input into an input port at the transmitting terminal is not transmitted to the filter at the receiving terminal but propagated via the antenna terminal. Also, the signal received by the antenna is transmitted to the filter at the receiving terminal so that an external energy is transferred to the receiving terminal.
FIG. 6 shows an insertion loss characteristic graph at the filter at the receiving terminal of the duplexer according to the prior art and the present invention. As shown in FIG. 6, in the duplexer according to the prior art, the attenuation characteristics are improved at the frequency band lower than the pass band width.
Although the above-mentioned duplexer improves the attenuation characteristics with the small number of resonators and the filter to have a pole, its size is large and a method for fabricating thereof is complicate because of the external elements, such as a chip capacitor and a chip inductor.
With the miniaturization of communication systems, it is required that the duplexer should be miniaturized and also that the duplexer have excellent attenuation characteristics at the frequency band lower than the pass band, so as to raise the efficiency in using frequency, by using the transmitting frequency which is in close vicinity to receiving frequency. However, because the duplexer employing the above-mentioned dielectric resonators, in the form of a monoblock type, is in need of a large number of resonators to improve the attenuation characteristics, the size of filter becomes larger. In case of the duplexer using the filter having a pole, filter""s size is large and a method for fabricating thereof is complicate because of the external elements, such as a chip capacitor and a chip inductor.
Therefore, it is an object of the present invention to provide a miniaturized duplexer by excluding external elements, such as a chip capacitor and a chip inductor.
It is another object of the present invention to provide an improved duplexer having excellent attenuation characteristics at lower frequency band than the pass band or at higher frequency band than that.
It is further another object of the present invention to provide a duplexer capable of being manufactured by simply processes to reduce its cost.
In accordance with an aspect of the present invention, there is provided a duplexer having stepped impedance resonators which are formed in a dielectric block coated with a conductive film, wherein the duplexer includes a transmitting filter, a receiving filter and an impedance matching circuit, the duplexer comprising: a) a plurality of open ended resonators arranged in a front side of the dielectric block, the open ended resonators includes: a-1) a plurality of first apertures, each of which passes through the dielectric block from an upper surface thereof to a bottom surface thereof, wherein inner surfaces of the first apertures are coated with the conductive film; and a-2) a plurality of uncoated gaps round the first apertures on the upper surface of the dielectric block, b) a plurality of shorted resonators arranged in a rear side of the dielectric block, the shorted resonators includes: b-1) a plurality of second apertures, each of which passes through the dielectric block from the upper surface thereof to the bottom surface thereof, wherein each shorted resonators corresponds to the open ended resonators and wherein inner surfaces of the second apertures are coated with the conductive film, c) a plurality of recesses formed at the bottom of the dielectric block, extending from the first apertures of the open ended resonators to the second apertures of the shorted resonators, wherein the recesses are coated with the conductive film; d) a plurality of first grooves for controlling receiving coupling at the receiving filter, each of which is formed in the rear side of the dielectric block at the receiving filter, wherein the first grooves are formed from the upper surface of the dielectric block to the bottom surface of the dielectric block; and e) a plurality of second grooves for controlling transmitting coupling at the transmitting filter, each of which is formed in the front side of the dielectric block at the transmitting filter, wherein the second grooves are formed from the upper surface of the dielectric block to the bottom surface of the dielectric block.
In accordance with an aspect of the present invention, there is provided a duplexer having stepped impedance resonators which are formed in a dielectric block coated with a conductive film, wherein the duplexer includes a transmitting filter, a receiving filter and an impedance matching circuit, the duplexer comprising: a plurality of resonators arranged in a rear side of the dielectric block, wherein each resonators passes through the dielectric block from an upper surface thereof to a bottom surface thereof, wherein inner surfaces of the first apertures are coated with the conductive film; a plurality of recesses formed at the upper surface of the dielectric block, extending from the resonators toward a front side of the dielectric block; a plurality of first grooves for controlling receiving coupling at the receiving filter, each of which is formed in an outer wall of the dielectric block and between the resonators wherein the first grooves are formed from the upper surface of the dielectric block to the bottom surface of the dielectric block; and a plurality of second grooves for controlling transmitting coupling at the transmitting filter, each of which is formed in the upper surface of the dielectric block and between the resonators, wherein the second grooves are formed from the rear side of the dielectric block to a front side of the dielectric block.